The invention relates to a shaft furnace, particularly to a direct-reduction shaft furnace, with a bed of lumpy material, particularly lumpy material containing iron oxide and/or sponge iron, wherein discharge openings for lumpy material are located above the bottom area of the shaft furnace and inlet ports for reduction gas above the discharge openings.
Many shaft furnaces, particularly reduction shaft furnaces of the aforementioned type, are known from prior art. Such a shaft furnace, which is essentially designed as a cylindrical hollow body, generally contains a bed of lumpy material containing iron oxide and/or sponge iron, with the lumpy material containing iron oxide being charged into the upper part of the shaft furnace. Reduction gas coming, for example, from a melter gasifier is injected into the shaft furnace and thus into the solid bed through several inlet ports arranged along the circumference of the shaft furnace in the area of the lower third of the shaft furnace. The hot, dust-laden reduction gas ascends through the solid bed, completely or partially reducing the iron oxide of the bed to sponge iron.
The completely or partly reduced iron oxide is extracted from the shaft furnace by means of discharge devices located between the bottom area of the shaft furnace and the area of the gas inlet ports. These discharge devices are usually designed as radially (related to the shaft furnace) arranged discharge screws.
The zone located in the area of the shaft bottom in which the discharge devices are arranged must have a maximum active discharge area in order to allow the bulk material to subside as uniformly as possible and to ensure continuous movement and mixing of the material in the reaction zone.
However, the small number of discharge devices and the involved space conditions have the disadvantage that part of the bulk material located in the plane of the discharge devices cannot be covered by these discharge devices so that nonmovable zones with very steep inner angles of repose are formed above these nonactive areas.
These zones, which are referred to as "dead man", have the disadvantage that a portion of the reaction space volume becomes partly inactive, active volume meaning the region of a shaft furnace where the desired gas-solid reactions occur.
As a result, cakings and agglomerates may form in these regions owing to the long dwelling times of ores and of already reduced ores, which impair the material flow and consequently reduce the material reaction and, thus, also the productivity.
The prior-art arrangement essentially features two zones above which "dead man" forms, that is, the central region not covered by the radially arranged discharge devices and another zone formed by two wedge-shaped regions located between two discharge devices each, wherein the bulk pyramids building up in these dead zones impede the solid flow and build up to a level where the reduction gas inlet ports are concealed by the bulk material that is building up and the dust freight of the reduction gas forms a bed that is relatively impermeable to gas. As a result, the required homogeneous gas distribution in the shaft furnace does not take place.
EP-B-0 116 679 describes screws for moving solid particles in a shaft furnace and for discharging such particles. These radially arranged and overhung screws are of identical length and have a cylindrical cross section. Although the dead corners between the screws are minimized by the installation of wedge-shaped baffles, "dead men" cannot be prevented from building up.
EP-B-0 085 290 reveals arrangements of short conical screws supported in a tapered baffle located in the center, which also serves as angle of repose, as well as along the circumference of the shaft furnace. Although the formation of a central "dead man" can be minimized through the wedge-shaped baffle located in the center, there are still inactive zones between adjacent discharge devices, which lead to the formation of undesirable bulk pyramids as already mentioned.
None of the arrangements of discharge devices and/or baffles known from prior art is capable of preventing the formation of bulk pyramids referred to as "dead man" between two adjacent discharge devices each at the inner edge of the shaft furnace.
Accordingly, the object of this invention is to avoid the formation of bulk pyramids between two adjacent discharge devices each at the inner edge of the shaft furnace or to reduce such formation to an extent that the tips of the bulk pyramids are located considerably below the area of the reduction gas inlet ports and the latter are no longer concealed by nonmovable bulk material.